An electron backscattered diffraction study on the dynamic recrystallization behavior of a nickel–chromium alloy (800H) during hot deformation

Abstract

The objective of the study described here is to evaluate the effect of temperature, strain rate, and strain on the microstructure of dynamically recrystallized nickel–chromium alloy (800H) subjected to hot compression over a wide range of strain rates. The microstructural evolution was studied by electron backscattered diffraction (EBSD) and the effect of adiabatic heating on hot deformation was analyzed to correct the flow curves at high strains. The grain orientation spread (GOS) approach was used to distinguish the dynamic recrystallization (DRX) grains from the deformed matrix. The nucleation mechanism of DRX and the role of Σ3n CSL boundaries during DRX were explored. Additionally, the influence of carbides on the DRX behavior was studied within the temperature of 850–950°C. The results indicated that the DRX can be stimulated by adiabatic heating and strong dislocation–dislocation interaction occurring with increase in the strain rate in the range of 1–30s−1. The threshold value of GOS (1.2°) separated the DRX grains from the deformed matrix. The recrystallized grains nucleated at pre-existing grain boundaries by extensive bulging associated with grain fragmentation. The Σ3n CSL boundaries play an important role in DRX and they can be generated through interaction among them after the initiation of DRX. The precipitation of Cr23C6 and Ti(C, N) at the parent grain boundary could restrain or even inhibit the occurrence of DRX in the temperature range of 850–950°C.